Silica-on-silicon planar lightwave circuit (PLC) technology is well established and provides a low loss and stable
photonic device platform. However, limitations in size and integration of active components remain. Engineering of the
layer structure in silica PLCs to achieve high-index contrast, compact device architectures and monolithically integrated
optical nonlinearities is described. Modeling of properties of doped-silica layers provides a design strategy for
optimization of waveguide loss and birefringence. Optical nonlinearities in poled silica layers have been demonstrated,
and recent work to incorporate these into functional device structures and exploit them for high speed modulation is
reported.